Problem: Before the previous stop there were 36 people riding on a train. 27 people ended up getting off at the stop. How many people are riding the train now?
Answer: The number riding the train now is the difference between the number who were riding and the number who got off at the previous stop. The difference is $36 - 27$ people on the train. $36 - 27 = 9$ people are on the train.